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Thread: Bulls eye glass

  1. #1
    Registered user. Les harland's Avatar
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    Default Bulls eye glass

    Were the "bulls eye glasses" used in older pocket watches a fashion or was it something to do with the way they were made?

  2. #2

    Default Re: Bulls eye glass (By: Les harland)

    Quote Originally Posted by Les harland View Post
    Were the "bulls eye glasses" used in older pocket watches a fashion or was it something to do with the way they were made?
    This earlier thread seems to have come to no conclusion. We are used to seeing pontil marks ground out on glassware but that may just have contributed to it as a fashion

    http://mb.nawcc.org/showthread.php?6...ye-PW-Crystals
    Nick, lots to learn, late starter.

  3. #3
    Registered user. Les harland's Avatar
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    Default Re: Bulls eye glass (By: novicetimekeeper)

    It is an interesting thread, Thanks Nick
    I tried the Forum Search feature but did not find it because I searched for "Bulls eye" not "Bullseye"

  4. #4

    Default Re: Bulls eye glass (By: Les harland)

    Quote Originally Posted by Les harland View Post
    It is an interesting thread, Thanks Nick
    I tried the Forum Search feature but did not find it because I searched for "Bulls eye" not "Bullseye"
    I searched google and that was one of the results.
    Nick, lots to learn, late starter.

  5. #5
    Registered User gmorse's Avatar
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    Default Re: Bulls eye glass (By: Les harland)

    Hi Les,

    I believe that it was more to do with fashion, and was mostly a late 18th and 19th century thing, because the earlier crystals were plain, without the ground flat portion in the centre. These high domed crystals were cut from a large blown glass sphere, so pontil marks weren't involved in the manufacturing process.

    Regards,

    Graham

    "Ut tensio, sic vis" - Robert Hooke

  6. #6
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    Default Re: Bulls eye glass (By: gmorse)

    if I remember correctly, this Liebig image was posted by Tom McIntyre.

    Click image for larger version. 

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    regards enrico

  7. #7

    Default Re: Bulls eye glass (By: eri231)

    At the beginning of the C19th given a blown glass sphere how would you produce a watch lens?

    1. set a diamond tipped compass to the radius of the required lens
    2. use a hard pointed implement to create a small indentation in the surface of the sphere
    3. use this as the centre and score a circle with the diamond tipped compass
    4. repeat 3 over the useable surface of the sphere
    5. carefully break out the circular pieces of glass
    6. grind and then polish out the indentations and finish the lens edge

    Result – bulls eye lens.

    Just a thought … I find it difficult to believe it was solely down to fashion and prefer to believe it was in some way related to the manufacturing process – but not necessarily my 'top of the head' suggestion.

    John

  8. #8
    Registered User gmorse's Avatar
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    Default Re: Bulls eye glass (By: John Matthews)

    Hi John,

    Your suggestion is possible, but the illustration clearly shows the work being done from the inside of the spheres.

    Regards,

    Graham

    "Ut tensio, sic vis" - Robert Hooke

  9. #9
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    Default Re: Bulls eye glass (By: gmorse)

    It is obvious that , working from the inside the cut was flat, to be inserted in the bezel.
    regards enrico

  10. #10

    Default Re: Bulls eye glass

    Hi John, having worked in the Optical Trade, (Did my Apprenticeship) in the 1950's with E Wood & Co., I think that this method would result in lots of shattered Spheres. In the Movies it looks easy, but it is not. I looked in a Drawer and I still have a Circular Cutter, the Rubber Pad has perished. I might fix it up as I need a Glass for a Mercer Bulkhead Clock that I am fixing up. Regards Ray [QUOTE]carefully break out the circular pieces of glass ATTACH=CONFIG]352704[/ATTACH]Click image for larger version. 

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    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Omexa; 08-06-2017 at 01:52 PM.

  11. #11
    Technical Admin Tom McIntyre's Avatar
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    Default Re: Bulls eye glass (By: Omexa)

    The thing that amazes me is that I have seen pictures of surviving spheres with most of the crystals cut from them but the sphere intact. That seems to prove that some of them were cut from the outside.

    I agree with the view that the bulls eye was a fashion trend of the late 18th and first half of the 19th century.

    The other thing one could do to understand this process better would be to measure the height and diameter of some of the very high dome crystals that still exist on the market and are often seen on the early 18 century watches. I suspect that those spheres were pretty small to start with to get the extreme curvature.
    Tom McIntyre Click me.
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    you won't have anything to laugh at when you're old.
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  12. #12
    Registered User gmorse's Avatar
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    Default Re: Bulls eye glass

    Hi Tom,

    Quote Originally Posted by Tom McIntyre
    ...I suspect that those spheres were pretty small to start with to get the extreme curvature...
    Yes indeed, only around 3 or 4 inches in diameter, or even less.

    It's not easy to make out the exact nature of the tools being used in that image in post #6.

    Philip Priestley wrote an article on the subject in the December 2009 issue of the Bulletin.

    Regards,

    Graham

    "Ut tensio, sic vis" - Robert Hooke

  13. #13

    Default Re: Bulls eye glass (By: gmorse)

    I love glass, but I'm rubbish at working it. I find the idea of making the spheres and cutting the circles amazing. I've seen watch glasses made by the slump method, such skill.

    I love finding glass in a longcase showing the circular rings from production.
    Nick, lots to learn, late starter.

  14. #14

    Default Re: Bulls eye glass (By: Les harland)

    Hi Tom, that sure must take some Skill.
    The thing that amazes me is that I have seen pictures of surviving spheres with most of the crystals cut from them but the sphere intact. That seems to prove that some of them were cut from the outside.
    Here is a Photo of how we cut different shaped Lens; you put different templates on the bottomClick image for larger version. 

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ID:	352727. We edged on a Sandstone Wheel going away from you in rotation using water on the Stone. We later used Diamond impregnated Wheels. Regards Ray

  15. #15
    Technical Admin Tom McIntyre's Avatar
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    Default Re: Bulls eye glass (By: novicetimekeeper)

    Quote Originally Posted by novicetimekeeper View Post
    I love glass, but I'm rubbish at working it. I find the idea of making the spheres and cutting the circles amazing. I've seen watch glasses made by the slump method, such skill.

    I love finding glass in a longcase showing the circular rings from production.
    I am not sure that anyone other than a chemist would recognize the term "watch glass" as a small dish used to monitor the evaporation process of a solution.

    I once bought a watch from a friend who had ground a "watch glass" to make a crystal for a late 18th century watch case. It was awfully thick and I replaced it with a correct crystal eventually.
    Tom McIntyre Click me.
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    you won't have anything to laugh at when you're old.
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